How do I import an old iPulse jacket into iPulse 3?

Export your favorite jackets from previous versions of iPulse
onto the desktop. Next, drag the jacket file onto the new iPulse
icon in the Dock and it will be imported, showing in the menu on
the first preference panel.

The image in the file won't be Retina resolution and can't be
converted automatically, so it may be a little fuzzy if you make
the window larger than 64x64 pixels.